The research is concerned with the role of multiple gene loci which determine the structures of organ specific enzymes with very similar but not identical enzymic properties. In particular the biochemical genetics of the alkaline phosphatases will be studied because previous work indicates that this set of enzymes provides a good model system pertaining to this not uncommon phenomenon. The biochemical, immunological and genetic characteristics of these enzymes in man and also other mammalian species will be examined in order to determine the number of gene loci involved, the differences between their products, their organ specificity and their degree of allelic variation in different species. The possibility of immunological maternal-fetal incompatibility will also be studied by a search for maternal antibodies to placental alkaline phosphatase determined by paternally derived genes in the fetus. This phenomenon could be the cause of certain complications of pregnancy and of fetal abnormality. Data on a wide range of human enzymes will be retrieved in order to assess the incidence of multilocus enzymes and determine their most characteristic features.